#include <cmath>
#include <cstdio>
#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;
int main() {
    int start,diff,min,total;
    cin>>start;
    cin>>diff;
    cin>>min;
    cin>>total;
    int count=start,ans=0;
    while(1){
    	if(count<=total){
    		start=start-diff;
    		if(start<=min)
    		start=min;
    		count=count+start;
    		ans++;
		}
		else
		{
			cout<<ans;
			break;
		}
	}
    return 0;
}